From a fish store, you can expect to pay 30+ for a small frag. If it is a nicer piece, then yes that is about right. I recently bought a frag from a guy on here for a red mille and it was 1 inch. It was 15 bucks but kind of disappointing because it's so small. I'm used to bigger pieces though but for 15 bucks, I guess you shouldn't expect much.
I tend to pick out the nicer ones so I end up paying more. However, alot of local reefers that have amazing tanks just want to thin it out so I get some pieces for cheap.